Mortgage Calculator
Estimate the monthly payment and total interest on a repayment mortgage.
Runs entirely in your browser — nothing you enter is uploaded.
The result is arithmetic from the figures you entered, under the assumptions listed below. It is not regulated financial advice and not an offer. Speak to a qualified adviser before making a decision.
How to use Mortgage Calculator
- Enter the loan amount you plan to borrow.
- Enter the annual interest rate your lender has quoted.
- Enter the term in years.
- Read the monthly payment and total interest figures on the right.
- Select "Show yearly table" below the chart to see the balance, interest and capital paid for each year of the term.
How this works
This is a standard amortizing loan. Each month you pay the interest that accrued on the outstanding balance, and whatever is left of the payment reduces the balance itself. Because the balance falls every month, the interest portion shrinks and the capital portion grows — which is why the early years of a mortgage repay so little of what you borrowed. The payment is solved so that the balance reaches exactly zero on the final month of the term.
M = P × [ r(1 + r)^n ] / [ (1 + r)^n − 1 ] where r = annual rate ÷ 12 and n = years × 12
Assumptions
- The interest rate stays fixed for the entire term. Most real mortgages fix for an initial period and then revert to a variable rate, which this does not model.
- Payments are made monthly, on time, with no overpayments, underpayments or payment holidays.
- The figure covers capital and interest only. Buildings insurance, property taxes, ground rent, service charges and mortgage protection are excluded.
- Arrangement, valuation and legal fees are not included, whether paid upfront or added to the loan.
Worked example
A £250,000 loan over 25 years at a fixed 4.5% annual rate.
- Loan amount
- £250,000
- Annual interest rate
- 4.5%
- Term
- 25 years
- Result
- £1,389.58 per month
Over 300 payments that comes to £416,874 in total, of which £166,874 is interest — around 67p of interest for every £1 borrowed. In the first month, £937.50 of the payment is interest and only £452.08 reduces the balance. By the final year that ratio has almost completely reversed.
How to read the result
The monthly figure is what leaves your account; the total interest is what the borrowing actually costs you. Compare the two across different terms before deciding: a longer term lowers the monthly payment but raises the total interest substantially, because you are borrowing the same money for longer. Shortening a 30-year term to 25 years typically raises the payment by a manageable amount while saving a large multiple of that over the full period.
Limitations
- Not an offer, a quotation, or a decision in principle. A lender's own figure will differ and is the only one that counts.
- Variable, tracker, offset and interest-only mortgages behave differently and are not modelled here.
- Affordability depends on income, outgoings, credit history and lender stress-testing against higher rates — none of which this calculates.
- This is a calculation, not regulated financial advice. Speak to a qualified mortgage adviser before committing.
Frequently asked questions
- Does the monthly payment include property taxes or insurance?
- No — it covers capital and interest only, as stated under the result. Buildings insurance, property taxes, ground rent, service charges and mortgage protection are extra and vary by property and provider.
- What if my mortgage has an initial fixed period and then goes variable?
- The calculator assumes one fixed rate for the whole term. For a typical 2- or 5-year fix followed by a variable rate, run it twice — once for the fixed period at the known rate, once for the remaining term at your best estimate of the future rate — and add the two together.
- Can I model overpayments?
- Not directly. The yearly table shows the standard schedule with no overpayments. As a rule of thumb, any overpayment reduces the balance immediately, which shortens the remaining term or cuts future interest — the earlier in the term you overpay, the larger that effect.